Fine beam electron gun



rag. EQ, 35333 Bernard c. Genauer, rhnmerphia, ra.; :serena to Farnsworth Television incorporated. San

Francisco, Calif., a corporation of California application may is, 193s. ser-nx No. 30,33: 2 Gianna (C1. 25o-21.5)

This invention relates to a method and appa-- ratus'ior the production of electron beams o very small cross secronarea. and particularly to -an inherently accurate method whereby the electron beams produced maybe made 'as small as 4 desired. n

Prment methods of producingr a restricted elec'- tron beamA employe diaphragmvprovidedwith an apertureof asze'suicient to pass. the desired beam. Th'e apertures are drilled. in the diaphragm but it is found that the aperture so formed is frequently imperfect. Slight imperfections in the apertures have more pronounced effeci: in small beams than in large. It is also true th'at'assmailer beams are required proper alinement o the parts o apparatus become practically impossible, and-the difhculty of constr'mxting-apu paratus by presenty methods for very small beam. production is prohibitive from a practical standpoint.

It is the principal object of my invention to provide a practical and economical method of producing electron beams of very small cross section. Another object of my invention is to provide an efcientA and electve method ol providing an electron beam diaphragm with an aperture o any desired degree of minuteriess.

A further object of my invention is to provide a new and novel method of constructing an electron beam producing apparatus.

Another object of my invention is to provide improved apparatus for the production of electron beams o very small cross section and of high quality.

Other objects and advantages will-become apparent as the description proceeds in connection with the accompanying ldrawing; in which the single ligure illustrates a cathode ray tube con.- structed in accordance vwith the principles oi my invention Y The drawing illustrates a tube I provided with a. fluorescent screen' 2 upon which an electron beam is projected by an electron gun or the like. Such guns-are well known in the art and may comprise a. cathode 3. an anode d, and a gridvB. The cathode may in turn comprise a lm 6 of an electron emitting substance. such as anoxide of barium or strontium. carried on the concave surface of a cup l', which cup is ln turn positioned ln heat-receiving relation to a filament B. Any suitable source of current may be provided for energizing filament 8,' which. when heated, frees electrons from the emitting substance.

The anode i may be o the well known beam canal type, providing entry port as at 2. ptli-l A sitioned to receive electrons from the concave surface. of cup l. to the hollow cylindrical canal ill. A diaphragm H is secured over the exit end of the 'anode and serves todeflne the cross sectional area oi -afbean'iv .passing therethrough toward the screen!` The grid 5` may be ringsh-aped'and s mounted with itsaxis-ias.nearlyas possible in coincidence -with the axis 'of the anode andln line with the cathode.:

in operation, electrons freed iron: the emitter S, areshot through the anode by applying sufcent voltage between the anode and the cathode, The grid 5 may be maintained at a. slightly negative potential with respect to the cathode and serves to direct the electrons toward port 9 of the anode. The eld through which the electrons pass into the canal of the cylindrical anode tends to focus the electron beam at the azls o the diaphragm end o1' the anode. the electrons passing through the canal in. straight. slightly converging lines along the axis o the cylinder. The aperture i2 of the diaphragm should have its center at the focal center of the beam -so that the most effective portion o the bearn may be milked, the portions of the diaphragm surrounding the aperture serving to catch the fringe electrons d' the beam, and permitting only e sharply defined beam to pass `oe3'o1'ui'the diaphragm. The beam. 3o. 'so produced' may be utilized to produce a curve.

on the screen 2 under control of dellector plates i3 in a well known manner.

Heretofore the aperture i2 has been drilled orl otherwise etected in the diaphragm prior to fixing the cathode. anode, and grid 'in operative relation in the tube. The result has been that accurate alinement of the aperture with the cen. trai axis of the electron beam required considerable adjustment and precision in assembly, and even so, an absolute alinement was most often impossible. very slight misallnernent may resuit in the beam being partially, if not entirely. directed upon the diaphragm rather than through its aperture.

In accordance with my invention. the aperture l2 l5 formed in the diaphragm il after, not before, the cathode and anode are placed in assembled relation. During assembly a thin metallic diaphragm il, of some such material as molybdenum or nickel. having no aperture thereln, is welded or otherwise fastened over the exit end of the beam canal l0. .The assembled tube ls then evacuated. The cathode is then heated and a. voltage applied to the anode i with the 2 f ,amaai result that s, beam o! electrons is on the diaphragm i! at the spot at whim an aperture should be mede. .es the roiage on the anode is increased, the spot by the electrons is correspondingly heated and, with suiiicient. heatingA of this character. the eiaphragm is punctured. Since the maximum heating occurs at the point. of greatest electron carb' eentra'tlon. the resuitant vpuncture is propery located, and, if the .anode voltage is reduced mmedately after the puncture occurs, the apemu'e remains smai. The sue of the aperture may be increased as desired by simply continuing the process so as to further melt the edges of the aperture until an aperture of the desired size is produced.

The Yotages used to puncture the diaphragm are large compared to, normal operating voltages.

Accordingly no change in aperture size oc'curs in normal operation.

Forming the diaphragmpaperture in this manner insures precision in aiinernent with' comparatively iittie e'ortand it 'also permits lha making oi`very minute apertures, for itis evident that the rst passage of electrons. through the diaphragm during the piercingstepoecm's at the-,centerof 'the beam. The fact of the pas` sage is immediateb' evident on the .screen` and vthe size of the-spot on the screen serves 's an. indication of the size of the aperture.

While-.I have disclosed my invention in oo ncomprises forming said anode without an aperture therein, focusing a beam o' electrons on l. predetermined spot on said anode, acceierating said electrons until `the anode is' pierced at the area of electron impact, and thereafter projecting electrons through said aperture and utilizing l said latter electrons.

2. In a cathode ray tube wherein abeam of electrons is projected .through an'apertured anode. the method of forming said apertura which comprises orzning a beam canal 'in -said mode closing one'lenri of said beam directingeiectrons into the open end of said' beam canal; accelerating said electrons to npact the' ciosed'endwith sufcent velocity to reopeniiie beam canal by meltingandY vaporizatori,v and thereafter passing electrons through said opening to obtain an indication.

BERNARD C. GARDNER 

